GEOLOGICAL INTRODUCTION 19 



In 'his classification of the Mississippian, Ulrich 1 has included the 

 Warsaw with the succeeding Salem or Spergen and St. Louis limestones 

 in the Meramec group. This grouping of the formations is not followed 

 here because the relationship of the Warsaw is manifestly closer with the 

 subjacent than with the superjacent formations. Lithologically there is 

 no satisfactory basis for differentiating the Warsaw from the subjacent 

 Keokuk, and the faunal relations of the two formations are very close. 

 In the typical expression of the two formations the Keokuk is essentially 

 limestone with subordinate shale beds, while the Warsaw is largely shale 

 with subordinate limestone beds; the transition from one formation to 

 the other being gradual, with no suggestion of an unconformity. The 

 fauna of the Warsaw does contain an element which is closely allied to 

 the faunas of the superjacent formation, but this fauna is notoriously a 

 recurrent element in our Mississippian series, occurring also well down 

 in the Keokuk, in the St. Louis quadrangle and elsewhere. 2 The absence 

 of the Warsaw formation south of St. Louis and the contact of the Salem 

 on the Keokuk, indicates a line of unconformity which is worthy of recog- 

 nition as a line of major subdivision in the Mississippian series. Uncon- 

 formable relations between the thin northern extension of the Salem and 

 the subjacent Warsaw are also indicated at Warsaw, Illinois. 3 



III. MERAMEC GROUP 



The Meramec group was established by Ulrich 1 to include the Warsaw, 

 "Spergen" and St. Louis formations, but in the present report it is used 

 to include the "Spergen" or Salem, and the St. Louis limestones, the 

 Warsaw formation being excluded and incorporated in the Osage group 

 for reasons which have already been discussed. In the older reports of 

 the Illinois Survey, by Worthen, this series of limestones was commonly 

 called the St. Louis group, but this name, although proposed many years 

 before the one here used, is inadvisable because the use of the same name 

 for a subordinate formation and for the group leads to much confusion 

 and therefore is not good practice. 



Salem limestone. 4 The Salem limestone has its typical development in 

 Indiana where it is the source of the well-known building stone which 

 goes on the market as "Bedford Stone." The name Bedford limestone 



1U. S. Geol. Survey, Prof. Paper, No. 24, p. 90 (1904); U. S. Geol. Survey, Prof. 

 Paper, No. 36, p. 24 (1905). 



2 Bull. U. S. Geol. Survey, No. 438, pp. 21 and 40 (1911). 



3 Bull. 111. State Geol. Survey, No. 8, pp. 83-88 (1908). 



4 Spergen limestone of Ulrich. 



